The present invention relates generally to methods and apparatuses for detecting leaks in fluid-conducting systems, and more particularly, to the detection of leaks in water-conducting systems that are used for cooling or heating pressurized types of devices such as blast furnaces, boilers, heat exchangers, heat treating furnaces, etc.
In the case of a blast furnace, a typical structure has an exterior metal shell lined with a refractory interior. Tuyeres or nozzles, for introducing combustion-supporting air into the blast furnace, extend into the furnace interior at a lower portion thereof. Located above the tuyeres are portions of the furnace known as the bosh, belly and stack, and located below the tuyeres is a furnace portion known as the hearth. All of these portions of the blast furnace are cooled with cooling members extending inwardly through the furnace shell and connected to respective cooling circuits through which cooling water is pumped.
In large blast furnaces, the number of separate cooling circuits may range from 500 to 1000. Each individual cooling circuit has an upstream end and a downstream end and includes one or more cooling members, usually less than ten. The types of cooling members include tuyeres having built in cooling jackets, tuyere coolers surrounding the tuyeres, per se, and copper plates or staves or other cooling members in the bosh, belly, stack and hearth. Each cooling member has an inlet for the cooling liquid, connected to the upstream end of the cooling circuit, and an outlet for the cooling liquid, connected to the downstream end of the cooling circuit, either directly or via the inlet and outlet of a downstream cooling member in the same circuit.
Because of the high temperature and severe reaction conditions inside the blast furnace, cooling members frequently develop leaks. In conventional cooling systems, the fact that there is a leak somewhere in the system can usually be discerned when the leak occurs. However, to isolate the leak to the particular cooling circuit in which the leak is located, using conventional leak-locating techniques, is a long, tedious and cumbersome procedure when the cooling system contains several hundred cooling circuits, as is often the case in modern blast furnaces. Indeed, it may take up to two to three days to isolate the leak, using conventional procedures.
It is important to rapidly detect such leaks. Failure to do so may cause chilling of the furnace by the injection of large volumes of cooling water into the furnace from the cooling member when water in the leaky cooling member is at a pressure higher than the furnace internal gas pressure. When the water in the leaky cooling member is at a pressure lower than the furnace internal gas pressure, failure to rapidly detect a leak may cause the loss of large amounts of combustible blast furnace gas into the cooling circuit and then into the cast house (a part of the blast furnace complex), and this creates safety problems. In addition, blast furnace gas entering the cooling system could be drawn into the pumping system and damage the pumps, and either furnace gas leaking into, or steam generated in a cooling plate that has or is about to fail, respectively, would decrease the cooling effectiveness of the cooling liquid in downstream cooling members in the circuit and, hence, potentially cause the formation of a leak in one or more of these downstream members.
With respect to prior art leak detection devices, numerous types of flowmeters and associated instrumentation have been developed for measuring fluid flow. (These include orifice meters, turbine meters, vortex meters, magnetic flow meters, etc. Hence, it would be possible to place one of these devices on the inlet line of each cooling circuit and another one of these devices on the outlet line of that circuit and utilize the difference in flow rates detected by the two devices to determine if there is any leakage in the circuit between the inlet and outlet flowmeters.
However, these devices are relatively costly. In addition, they usually create an obstruction in the fluid line which not only causes an additional pressure drop but, also, can promote the buildup in that line of foreign solid particles which could ultimately block the circuit. Also, these devices usually require frequent calibration, and the flow rate difference between the inlet and outlet readings is usually not very accurate.